Power Platform Community Forum Thread Details

I have a power app which people use to scan in and scan out of the building, they use a tag or manual input (mostly a tag with NFC) to check in or check out.

The data is saved in a simple dataverse table with the following columns:
Scancode / StartDate / StartTime / EndDate / EndTime

They scan a code from an NFC tag, which is entered in a text input control in my app. On the OnChange, it checks the following things (see code below):

if it is a valid tag (code)
If they haven't clocked in the past 30 seconds.
Depending on whether they checked in or out the last time, it moves to a different success screen.
1. If they checked out they move to a checkout screen;
2. If they checked in they moved to a checking screen.
In addition, it calculates the hours between start end now()

However, in our testing fase, people are experiencing that they need to scan twice. First time, they move to the succes screen, but it isnt patched to the database. Second time it works.
The issue doesn't happen with everybody and i cannot see a pattern.

Can somebody help me with this issue?

Below my code.

Set(varScanCode, Trim(Self.Text));

UpdateContext({ ScanCode: varScanCode, varSpinner: true });

If(

IsBlank(LookUp(ExtraEmployees, 'Tag Nummer' = varScanCode)),

UpdateContext({ varLabel: "Invalid code, please scan again!" }),

Set(varLastPatch, Blank());

Set(varMedewerkerPersnr, LookUp(ExtraEmployees, 'Tag Nummer' = varScanCode).Persnr);

With(

{

OpenRecord: LookUp(KloksysteemLogs, code = varScanCode && IsBlank(EindTijd)),

LastUpdate: First(SortByColumns(Filter(KloksysteemLogs, code = varScanCode),"modifiedon",SortOrder.Descending)).'Modified On'

If(

!IsBlank(LastUpdate) && DateDiff(LastUpdate, Now(), TimeUnit.Minutes) < 0.5,

UpdateContext({varLabel:"You can only clock in or clock out again 30 seconds after your last action."}),

If(

!IsBlank(OpenRecord),

// Clock out

Set(

varLastPatch,

Patch(

KloksysteemLogs,

OpenRecord,

{

code: varScanCode,

EndDate: DateValue(Now()),

EndTime: Now(),

Uren: Round(DateDiff(OpenRecord.StartTime, Now(), TimeUnit.Minutes)/60, 2)

}

)

);

Navigate(SuccesScreenOut, ScreenTransition.Fade),

// Clock in

Set(

varLastPatch,

Patch(

KloksysteemLogs,

Defaults(KloksysteemLogs),

{

code: varScanCode,

StartDate: DateValue(Now()),

StartTime: Now(),

EndDate: Blank(),

EndTime: Blank()

}

)

);

Navigate(SuccesScreenIn, ScreenTransition.Fade)

)

Categories:

Error handling

Microsoft Dataverse with Power Apps

Hi ,

TextInput.OnChange is unreliable for scan logic because it can fire multiple times and at unpredictable moments.

With NFC or scanner input, the value may arrive in parts, or the event can be retriggered by focus changes, resets, or navigation.

Since Patch() is an async Dataverse call, Navigate() can run even if the write has not completed or has failed, which leads to the “success screen but no record” scenario.

Microsoft documents OnChange as an edit-detection event, not a guaranteed single action trigger, which makes it unsuitable for transactional logic.

A better pattern is to use the text input only to capture the value (for example via TextInput1.Text or a variable) and move all logic to a button’s OnSelect. A button executes once, is easy to disable while processing, and allows you to store the Patch() result in a variable and validate it before navigating. This makes the flow deterministic.

When you use Set(varResult, Patch(...)), Power Fx/ power apps runtime waits for the Patch operation to complete and then stores the returned record in the variable